In recent years, the spread spectrum (SS) technology has been widely used in various wireless communication systems. The main technical feature of SS communication is that the radio frequency (RF) bandwidth used for signal transmission is considerably larger than the bandwidth of data. In practice, a transmitter spreads the data transmitted to a very wide frequency band by use of a pseudo noise code (PN code), while a receiver restores the data transmitted by use of the same PN code. With the aforesaid operations, SS communication exhibits good interference immunity and a good anti-interception ability, and has a very good performance even under extremely poor channel conditions.
In implementation of an SS communication system, synchronization is one of the very important steps, and more importantly, PN code synchronization is the primary step to establish SS communication. The PN code synchronization is achieved by tuning a PN code generator of the receiver in such a way that a difference between the phase of the PN code generator and the phase of the PN code received is less than one chip. Since PN codes have a good autocorrelation property, the PN code phase difference can be determined according to a magnitude of a value output by a correlator. If the PN code phase difference is zero (i.e., the two PN code phases coincide with each other completely), then the signal output by the correlator is the strongest. Otherwise, if the PN code phase difference exceeds one chip, then the correlator outputs a signal that is similar to a noise.
To make the operation of PN code synchronization less complex, the PN code synchronization may be divided into two stages, that is, a PN code acquisition stage and a PN code tracking stage. The PN code acquisition stage is to find the correct code phase through code phase searching so that the PN code phase difference is controlled to be less than one chip (usually set to be 0.5 chips). For the PN code acquisition stage, the efficiency of the code phase searching is a key factor that affects PN code synchronization.
Accordingly, an urgent need exists in the art to provide a solution capable of performing code phase searching efficiently in the PN code acquisition stage.